Field of the Invention
The present invention relates to a printing apparatus and a substrate for driving a light-emitting element.
Description of the Related Art
An electrophotographic printing apparatus (such as a laser printer) includes, for example, a light-emitting element for irradiating a photosensitive drum with a laser beam. First, the light-emitting element irradiates, based on printing data, the charged photosensitive drum with the laser beam. This lowers a potential of a portion in the photosensitive drum irradiated with the laser beam, and a potential distribution based on the printing data is formed on the photosensitive drum (latent image). Next, toner as toner particles is attached to this photosensitive drum. The toner attached to the photosensitive drum follows (develops) the potential distribution on the photosensitive drum. Then, an image according to the printing data is formed on a printing medium such as a paper sheet by transferring the toner that has attached to the photosensitive drum to the printing medium.
Some printing apparatuses control driving of the light-emitting element so as to maintain the laser beam of a suitable light amount (target value). This control is also referred to as Auto Power Control (APC). A printing apparatus having an APC function includes, for example, a light-emitting element, a light-receiving element which receives light from the light-emitting element, a monitor which receives a current from the light-receiving element, and a driving unit which drives the light-emitting element. The driving unit holds a monitoring result from the monitor in APC and drives the light-emitting element with a driving force based on the held monitoring result in subsequent printing.
FIG. 1 in Japanese Patent Laid-Open No. 2012-38959 discloses the circuit arrangement of a feedback system with a current-current converter being arranged between a comparator corresponding to the above-described monitor and a light-receiving element. More specifically, in APC, a result obtained by converting a current (monitor current) from the light-receiving element with the current-current converter is fed back to the comparator. According to this arrangement, however, a delay is caused in the above-described feedback system by converting the monitor current with the current-current converter.